E-37 Horn Does Not Sound - Komatsu PC88MR-10 Shop Manual

E-37 Horn does not sound

Failure Horn does not sound.
Related
information
No. Cause
Defective fuses F01-5
1
and F01-8
Defective horn relay
2 (Internal open or short
circuit)
Defective diode array
D03
3
(Internal short circuit)
Defective horn switch
4
(Internal open or short
circuit)
Defective horn (M07)
(Internal open or short
5
circuit)
Defective wiring
6
harness
Open circuit in wiring
harness
7
(Wire breakage or
defective contact of
connector)
Ground fault in wiring
harness
8
(Contact with ground
circuit)
Defective horn
9
(Internal defect)
PC88MR-10
(PC88MR-KA2-400-A-Z0-A)
Procedure, measuring location, criteria, and remarks
If fuses F01-5 and F01-8 are blown out, the circuit probably has ground fault.
In this case, perform check on cause 8 first.
1. Turn starting switch to OFF position.
2. Replace horn relay (connector: R08) with another relay.
3. Turn starting switch to ON position.
4. Press horn switch.
If horn sounds, original horn relay is defective.
1. Turn starting switch to OFF position.
2. Remove diode array and connect T-adapter to male side.
a Measure it in diode range.
Between D03 (male) (8) (+) and (4) (-)
Continuity
Between D03 (male) (4) (+) and (8) (-)
1. Turn starting switch to OFF position.
2. Disconnect connector M22 and connect T-adapter to male side.
Between M22 (male) (1)
Resistance
and (2)
1. Turn starting switch to OFF position.
2. Disconnect connector M07 and connect T-adapter to male side.
Continuity Between M07 (male) (1) and (2)
1. Turn starting switch to OFF position.
2. Disconnect connector M07, and connect T-adapter to female side.
3. Turn starting switch to ON position.
4. Press R.H. knob switch.
Voltage Between M07 (female) (1) and (2)
1. Turn starting switch to OFF position.
2. Disconnect connector R08, and connect T-adapter to female side.
Continuity Between R08 (female) (5) and ground
a If no failure is found by check on cause 6 or preceding check, this check is
not required.
1. Turn starting switch to OFF position.
2. Remove fuse F01-5 and F01-8
3. Disconnect connectors R08 and M22, and connect T-adapters to each
female side.
Between F01-8 and M22 (female) (1)
Between M22 (female) (2) and R08 (female) (1)
Resistance
Between R08 (female) (2) and ground
Between R08 (female) (3) and F01-5
a If fuse is not burnt out, this check is not required.
1. Turn starting switch to OFF position.
2. Remove fuse F01-5 and F01-8
3. Disconnect connector R08, M07, M08, and connect T-adapter to female
side.
Between R08 (female) (1) and ground
Between R08 (female) (3) and ground
Resistance
Between R08 (female) (5) and ground
If no failure is found by preceding checks, horn may be defective.
40 Troubleshooting
Troubleshooting of electrical system (E-mode)
Switch: OFF
Switch: ON
Continuity
No
continuity
Min. 1 Mz
Max. 1 z
Continuity
20 to 30 V
Continuity
Max. 1 z
Max. 1 z
Max. 1 z
Max. 1 z
Min. 1 Mz
Min. 1 Mz
Min. 1 Mz
40-431